Automatic telephone system



May 6, 1941. w.'r. POWELL AUTOMATIC TELEPHONE SYSTEM- 9 Sheets-Sheet 1Filed Sept. 21, 1939 I N VE N TOR w/A/heso TROWELL ORNEY.

y 1941- w. T. POWELL AUTOMATIC TELEPHONE SYSTEM 9 Sheets-Sheet 5 FiledSept. 21, 1939 m2 m mh\ 3 o M I m m 93 vw S W I I III E Ro m \Q m? w M1| I w ma Q 1 3 A I I I I l I I I I L 2 g1 W M Q NQ II A. A. A. A L JQQ93 .1 L 1* 1- I I T II I Ill M may L m A A vvl L1 Yb II-r l I I I I Il.- I I I I 2 mm Si :2 3? m2 ATTORNEY.

w. T. POWELL 2,241,158 AUTOMATIC ,TIEILEPHONE SYSTEM Filed Sept. 21,1939 9 Sheets-Sheet 4 Q Q L w I 9 \h 3 T: I. I Q Q Q Q Q Q Q Q I kQ T iT T Y N MM I L (I L QN\ B w m mw I r. L I TI v I I Li- I i IT I I I I TI I I I I I I I I ll .l

May 6, 1941.

I I I I l I I I I l l I I l I I I l I I I I I I I I l I I I I L:- LI- LI I m I 2 :3 I I I I I I I I I I INVENT OR. WIN/EEO T POWELL ATTORNEY.

W.IT. POWELL 2,241,158

AUTOMATIC TELEPHONE SYSTEM Filed Sept. 21, 1939 I 9 Sheets-Sheet aW/NFEED I POWELL ATTORNEY.

May 6, 1941.

May 6, 19 41.

w. 'r. POWELL AUTOMATIC TELEPHONE SYSTEM Filed Sept. 21, 1939Sheets-Sheet 6 INVENTOR.

. B MtE 45m m WINFRED T. Fol/ELL ATTORNEY.

May 6, 1941.

w. r. POWELL' AUTOMATIC TELEPHONE SYSTEM Filed Sept. 21, 1939 9Sheets-Sheet 'T ATTORNEY.

y6,1941 w. T. POWELL 2,241,158

AUTOMATIC TELEPHONE SYSTEM ATTORNEY.

y 1941- w. 'r. POWELL AUTOMATIC TELEPHONE SYSTEM 'Filed Sept. 21, 1939 9Sheets-Sheet 9 TUTUTGTUT LfirUrUrUw U TU TU TU T mummm INVENTOR.Wl/VFRED TJPOWfLL BY A ATTORNEY.

INN

Patented May 6, 1941 S PATENT OFFICE AUTOMATIC TELEPHONE SYSTEM Winfred'1. Powell,

Rochester, N. Y., minor to The Stromberg-Carlson Telephone ManufacturingCompany, Rochester, N. Y., a corporation of New York- ApplicationSeptember n, 1939, Serial No. 295,925

11 Claims.

This invention relates to telephone systems and more particularly toautomatic telephone systems.

In automatic telephone systems of the type in which relays are employedas switching means a for completing a part or all of the telephoneconnections, provision must be made for completing trunk calls to andfrom a distant exchange. In such an arrangement provision mustpalso bemade at the local exchange for transferring a trunk call originating ata distant exchange from one substation at the local exchange to anyother desired substation thereat, the trunk in use being held during thetransfer operation. Provision must also be made for releasing aconnection from a calling substation to a busy called substation whilesignalling the calling substation of the busy condition.

The present invention ha for its purpose the improvement in suchautomatic telephone systems by the provision of novel circuitarrangements for meeting the above-mentioned conditions.

The drawings diagrammatically represent a telephone system when Figs. 1,2, 3 and 4 are arranged end to end in order, reading from left to right,and when Fig. is placed below Fig. 4 and with Figs. 5, 6, '7, 8 and 9placed end to end and arranged to read from right to left.

In these drawings Fig. 2 represents a call substation and its telephoneline, and

Fig. 2a represents a portion of employed in a code call arrangement;

Fig. 3 represents a portion of a trunk circuit which terminates at adistant exchange represented by the dotted rectangle;

Figs. 4 and 5 when taken together indicate a call substation at atelephone line as well as a relay connector and certain oi the commonequipment;

Fig. 6 represents a counting relay arrangement in which impulses dialedby the calling subscriber are counted and by which a relay connector isselectively operated;

Fig. 7 represents the major portion .of a link connector utilized inextending a telephone connection;

the circuits Figs. 1 and 8 represent a relay finder arrangement forconnecting the telephone lines to links and to trunk circuits; and

Fig. 9 represents a lock-out arrangement whereby originating ,calls are.extended in sequence. This figure in the lowerright hand corner thereof,also illustrates a relay allotter which functions to assign idle linkcircuits for use in sequence. It is believed thatthe invention will bestbe understood by describing the operation of establishing a connectionfrom a calling subscribers line such as that designated #11 (Fig. 2) toa called subscriber's line herein designated #41. When the callingsubscriber removes his receiver from the switchhook to initiate a call,a circuit is completed for the line relay 5 of this line. This circuitis traceable from the negative pole of battery, winding of the linerelay 5 (Fig. 9), conductor 6, back contact and armature of relay l,inner back contact and armature of the cutoff relay 8, telephone lineconductor 9, thence through the calling substation circuits of thecalling subscriber, telephone line conductor ll, outer armature and backcontact and cutofi relay 8 to positive pole of battery. The line relay 5when energized completes a lockout circuit whereby all of the remainingtelephone lines of the group are disabled from making a connection untila link is extended to the calling telephone line and whereby a finder ofthe relay type extends a link to the calling subscribers line. Theoperation of the relay type finder is completed in a very brief intervalof time so that the looking out of the remaining lines of .the group isnot seriously objectionable. It will be appreciated that the lock-outarrangement is provided in order that two simultaneously originatedcalls will not be coupled to the same link.

The mentioned lock-out circuit is completed for the tens lock-out relayl2 and for the units lock-out relay l3. It will be appreciated that thetens lock-out relay i2 is common to all telephone lines of .the grouphaving the numeral one as a tens digit designation, whereas the unitslock-out relay I3 is common to all telephone lines of the group havingthe numeral one as a units digit designation. The operating circuit forthe units lock-out relay i3 and for the tens lock-out relay i2 istraceable from the positive pole of battery, continuity spring and backcontact of the relay l2 and thence thru the corresponding continuitysprings and back contacts of the remaining tens lock-out relays of thisgroup, namely relays l6, l5, l6 and I1, conductor l8, inner back contactand continuity spring of the relay l2, winding of this relay, conductor19, front contact and armature of line relay 5, conductor 20, winding ofthe units lock out relay I3, its inner continuity spring and backcontact, conductor 2i, outer back contacts and continuity springs ofunits lock-out relays 22, 23, 24, 25, I3 and resistance to the negativepole to the battery. The lock-out relays l2 and I3 are energized in thiscircuit and complete a locking circuitfor themselves from the negativepole of battery, inner armature, front contact and winding of the unitlock-out relay l3, conductor 28, front contact and armature of the linerelay 5, winding of the tens lock-out relay I2, its inner front contactarmature to the positive pole of the battery. While the tens lockoutrelay l2 and. the units lock-out relay l3 are thus held energized noother lock-out relays of the group can be energized since theirenergizing circuits are interrupted at the outer continuity springs andback contacts of the relays l2 and I3. T

As soon as the lock-out relays I2 and I3 are energized, the relay'2'l(Fig. 9) of a link allotter of the relay type is energized from thenegative pole of battery, winding of the relay 21,- back contact andarmature of the relay 28, conductor 23, front contact and armature ofthe look-out relay l2, conductor 38, armature and front contact of therelay l3, to the positive pole of battery. The allotter relay 2'! whenthus energized, completes circuits for operating the tens finder relay3| (Fig. 8) and the units finder relay 32. The circuit for the relay 3|is traceable from the negative pole of battery, winding of the relay 3|,conductor 33, armature and front contact of the relay I2, conductor 34,armature and back contact of the relay 28, uppermost front "contact andarmature of the relay 21 to the positive pole of battery. The unitsfinder relay 32 has lts circuit likewise traceable from the negativepole of battery, winding of the relay 32, conductor 35, armature andfront contact of the units lock-' out relay l3, conductor 36, armatureand back contact of relay 38, inner front contact and armature of relay'2'! to the positive pole of battery. With the tens finder relay 3| andthe units finder relay 32 energized, the tip conductor 31, the ringconductor 38 and the sleeve conductor 33 are extended thru the contactsof the units finder relay 32 and the tens finder relay 3| to thecorresponding conductors 48, 4| and 42 of the allotted trunk or linkcircuit. The extension of the calling line conductors 31 and 38 to thelink conductors 48 and 4|, completes a circuit including theseconductors in series with the upper and lower windings of thedifferentially wound relay 43 (Fig. '7) and of the calling bridge relay44 which also serves as an impulse relay. The relay 44 is energized inthe circuit but the differentially wound relay 43 is not operated atthis time. On the operation of the relay 44 the slow releasing relay 45is energized from the negative pole of battery, winding of this relay,middle front contact and armature of the relay 44, conductor 46, backcontact and armature of the trunk release relay' 41 to the positive poleof battery. When the relay 45 is operated it closes an obvious operatingcircuit for the relay 55. Also as soon as slow releasing relay 45 isoperated, it closes a locking circuit for the tens to the positive poleof battery. The operation of the relay 45, thru its armature 52 andfront line to an allotted link circuit.

contact, connects .the positive pole of battery through the winding ofthe relay 53, to the sleeve conductor 42 of the link. This sleeveconductor, on the'operation of the relay finder is connected to thesleeve conductor 39 of the calling line and this last-named conductor isconnected thru the right-hand armature and back contact of the r y 1 (Fi2), winding of the cutofl relay 8 to the negative pole of battery. Thecutofl relay is thus energized and thru its innermost front contact andarmature completes a locking circuit for itself independently of thecontrol of the relay 1. The operation of the cutoff relay 8 alsodisconnects the line relay 5 from its related telephone line. Relay 5thereupon releases and efiects the release of the look-out relays l2 andi3 so that they are again in readiness to cooperate in extending anothertelephone calling Although the operations just described in extending acalling line to a link appear rather involved, they are effected in amatter of a fraction of a second. As soon as the cutoff relay operates,the slow releasing relay I is energized from the negative pole ofbattery, righthand winding of this relay, front contact and armature ofcut-off relay 8 to the positive pole of battery.

It will be recalled that the relay 2! of the link allotter was operatedfollowing the initiation of the call to effect the operation of the tensfinder relay 3| and the units finder relay 32 in order to connect thecalling line to the link. On the operation of the relay 55, which wasefiected as soon as the slow releasing relay 45 was energized, a circuitwas completed for operating the number one allotter relay 28. Thiscircuit extends from the negative pole of battery, lower winding ofrelay 28, conductor 56, lower front contact and armature of relay 55 tothe positive pole of battery. Relay 28 when thus operated is lockedactuated in a circuit from the negative pole of battery,'upper windingof this relay, its inner front contact and armature, back contact andarmature of relay 51, which is the number 4 allotter relay of theseries, to the positive pole of battery. Thus, on the next originatingcall, the relay 58' (Fig. 9) which is individual to the number two linkwill respond in a manner similar to the operation of the relay 21 whichoperated as previously described to extend the calling line to thenumber one link. It will be understood that the relays 59 and 60 willoperate and lock in succession to allot the next link circuits in thegroupfor connection to other telephone lines. However, when the relay 5!associated with the last link of the group is operated, it interruptsthe locking circuits of the previously operated allotter relays so thatthey allot their individual link in succession.

As soon as the relay 45 was energized in response to the completion ofthe connection of the calling line to the allotted link circuit, therelay 5! (Fig. 6) associated with the counting relays of theconnectorwas energized. The energizing circuit for the relay 5! is traceable fromthe negative'pole of battery, winding of the relay 51, innermost lowerback contacts and armatures of the counting relays 58 to 63 inclusive,conductor 64, upper armature and back contact of relay 55, conductor 66,upper armature and back contact of relay 49, conductor 81, back contactand armature 88 of relay 69, conductor 18, upper front contact andarmature of relay 45 to the positive pole of battery. When the relay 5!is operated it applies a dial tone thru its front nected to an idle linkcircuit in the manner described and has received the dial tone, thecalling subscriber operates his dial impulse sender to transmit severalseries of code impulses corresponding to the respective digits of thewanted party's line. Let it be assumedthat the called subscribers lineis designated number 4|. The calling subscriber first operates hisimpulse sender to transmit four impulses, that is, the line circuit willbe interrupted four times and after a pause it will be interrupted onceto transmit an impulse corresponding to the units digit one. In responseto each of the four tens impulses, the calling bridge relay 44 releasesand attracts its armature four times. However, the slow releasing relay45 remains operated during the sending of this series'oi impulses.

When the impulse relay 44 releases in response to the first interruptionof the line circuit corresponding to the first impulse of the tensdigit,,the relay 44 releases. This causes the energization of the numberone counting relay 58, from the negative pole of battery, windin of thisrelay, conductor 1i, uppermost front contact and armature of relay 51,conductor 12, armature and back contact of the pulse lock relay",conductor 14, uppermost front contact and armature ofrelay 55, uppermostarmature and back contact oi'relay 44, conductor 15, up-

per armature and back contact of the release relay 49, conductor 81,back contact and armature 88 of the cut-in relay 88, conductor to thepositive pole of battery at theupper armature and front contact of relay45. The number one counting relay when thus energized, closes a lockingcircuit for itself from of battery, its winding, its innermost, lowerfront contact and armature and thru the innermost back contacts andarmatures of the counting relays 58 to 63 inclusive, conductor 64, backcontact and armature of relay 65, conductor 56, armature and backcontact of relay 49, conductor 61, back contact and armature 68 of relay69, conductor 10 to the positivepole of battery at the front contact andarmature of relay 45. A locking circuit is also completed for the relay51 from the negative pole of battery, winding of this relay, its innerfront contact and armature, conductor 16, front contact and armature ofrelay. 55, back contact and armature of relay 44, conductor 46,backcontact and armature of slow releasing relay 41 to the positive poleof battery. "When'the impulse relay 44 operates after the first impulsejust described, the relay 51 is released since its holding circuit isinterrupted at the armature and back contact of the mentioned relay .44.The number one counting 'relay 58 however remains energized since itsholdering circuit is independent of the relay 44.

When the impulse relay 44 is again deenergized in response to the secondimpulse of the tens digit, the number two counting relay 59 is energizedfrom the negative pole of battery, winding of this relay, conductor 11,front contact and armature of relay 58, uppermost back contact andarmature of relay 51, conductor 12, back contact and armature of relay13,

conductor 14, uppermost front contact .and armature of relay 55,uppermost armature and back contact of relay 44, conductor 15, armatureand back contact oi relay 49, conductor 81,-back the negative pole 'tureof the relay 41.

contact and armature 58 of the cut-in relay 69, conductor 10, frontcontact and armature of relay 45 to .the positive pole of battery. Thenumber two counting relay 59, when thus energized, closes a lockingcircuit for itself from the negative pole oi battery, winding of thisrelay, its innermost lower front contact and armature, innermost lowerback contacts and armature of relays 60 to 88 inclusive, conductor 64,back contact and armature of relay 55, conductor 66, upper armature andback contact of relay 49, conductor 51, back contact and armature 68 ofrelay 69, conductor 10 to the positive pole of battery at the upperfront contact and armature of relay 45. The locking circuit for therelay 58 is now interrupted at the innermost lower back contact andarmature of the relay 59 but before the number one counting relay 58releases, a substitute locking circuit is closed for itself from thenegative pole of battery, winding oi the relay 58, its innermost upperfront contact and armature, inner back contact and armature of relay 51,conductor 16, front contact and armature of relay 55, back contact andarmature of relay 44', conductor 46 to the positive pole of battery, atback contact and arma- This last-described circuit locks .the number onecounting relay in operated condition until the relay 44 is againenergized at the conclusion of the number two impulse of the tens digit,at which time it releases.

In response to the third impulse of the tens digit, the number threecounting relay 60 is operated and locked operated in the mannerpreviously described while the number two counting relay will be heldoperated until the impulse relay 44 is again operated at the conclusionof the third impulse, at which time it releases. Similarly, in responseto the fourth ten series of impulses.

impulse, the number four counting relay 6| is energized and is lockedoperated over circuits similar to those already described. When theimpulse relay 44 is operated at the conclusion of the fourth impulse,the number three counting relay 60 releases but the fourth countingrelaytl is maintained operated at this time. In the course of thetransmission of the four impulses corresponding to the tens digit, therelays 51, 58, 59, 60 and GI are operated and releasedin turn, with theexception of the number four counting relay 6! which is held operateduntil the tens connector relay is operated in the manner to bedescribed. It will be noted that there are no time margins or marginalrelay operations in this counting circuit since each relay is operatedin turn in response to the transmission of each impulse from the dialsender at the subscriber's station and during the closed circuitintervals between impulses, a preceding counting relay of the series isreleased to close a break point in the operating circuit for the nextcounting relay in the series to be operated by the next impulse.

The change-over relay 11 is operated in response to the first impulse ofthe tens digit and owing to its slow releasing characteristics ismaintained operated during the sending of the The circuit for thusoperating change-over relay 11, extends from the negative pole ofbattery, winding of this relay, conductor 14, uppermost front contactand armature of relay 55, uppermost armature and back contact of theimpulse relay 44, conductor 15, upper armature and back contact of relay49, conductor 61, back contact and armature 68 of relay 68, conductor 18to the positive pole of battery at the front contact and armature ofrelay 46. At the conclusion of the sending of the four impulsescorresponding to the tens digit as a result of which the number fourcounting relay 6| has been operated and locked operated, the impulserelay 44 will be energized for a suflicient period so that thechange-over relay 11 will release, its operating circuit beinginterrupted at the uppermost armature and back contact of the impulserelay 44. v

As soon as the change-over relay 11 releases, a circuit is completed foroperating the fourth tens connector relay 18. Since the number fourcounting relay has beenoperated, the operating circuit for the connectorrelay 18 extends from the negative pole of battery, winding of thisrelay, conductor 18, lowermost front contact and armature of the numberfour counting relay 6|, lowermost back contacts and armatures of therelays 68, 68, 68 and 61, back contact and armature of relay 88,conductor 8|, armature and back contact of change-over relay 11,conductor 82, back contact and armature 68 of relay 68, conductor 18 tothe positive pole of battery at the front contact and armature of relay46. The connector relay 18 when thus operated closes a locking circuitfor itself from the negative pole of battery, winding'of this relay, itsinner front contact and armature, conductor 83, inner front contact andarmature of relay 46 to the positive pole of battery. Also as soon asthe connector relay 18 is operated, a circuit is 'closed for the leaseof the relay 66interrupts the initial operating circuit for the transferrelay 88, which circuit extended thru its upper winding. However, therelay 88 is now locked operated thru its lower winding, but the'change-over relay 11 releases.

Also as soon as the relay 66 releases, a circuit is closed thru the backcontacts and armatures of counting relays 68- to 63 inclusive, foroperating the relay 61 which circuit is identical with that previouslydescribed as completed prior to the sending of the tens series ofimpulses. With the relay 61 again energized, the series of countingrelays are in readiness to count the series of impulses corresponding tothe units digit.

Since it has been assumed that the units digit is one, the impulsesender at the calling subscriber's station transmits one impulse inresponse to which the impulse relay'44 retracts its armatures. When thistakes place, the number one counting relay 68 is operated and lockedoperated over circuits identical with those previously described inconnection with the counting of the tens digit series of impulses. Itwill be recalled that the operating circuit for the numher one countingrelay extends from the negative 'pole of battery, winding of this relay,conductor winding of this relay, its lower front contact and ture ofrelay 18, conductor 85, to the positive pole of battery. The operationof the relay 66, at its armature and back contact, interrupts thepreviously described circuit which has been holding the number fourcounting relay 6| operated so that this counting relay now releases andthe series of counting relays is in readiness for operation in countingthe impulses corresponding to the units digit. The release of the numberfour counting relay 6|in the manner just described completes a circuitfor operating the transfer relay 88. This circuit extends from thenegative pole of battery, winding of the change-over relay 11, conductor14, armature and back contact of relay 18, conductor 12, armatures andback contacts of relays 61 to 63 inclusive, conductor 86, upper windingof the transfer relay 88, front contact and armature of relay 66,conductor 66, armature and back contact of release relay 48, conductor61, back contact and armature 68 of relay 68, conductor 18 to thepositive pole of battery at front contact and armature of relay 46.Change-over relay 11 is also energized in this circuit with the transferrelay 88, but the operation of the change-over relay 11 performs nouseful function at this time. The transfer relay armature and throughthe lower back contacts and armatures of relays 68, 68, 8|, 62 and 63and thence to the positive pole of battery over the conductor 64 aspreviously described.

With the number one counting relay 68 thus operated and change-overrelay 11 released, a

circuit is completed for the number one units connector relay 81, fromthe negative pole of battery, winding of the relay 81, conductor 86,

front contact and armature 88 of relay 68, back contact and armature ofrelay 61, middle front contact and armature ofjthe transfer relay 88:inow operated) conductor 8|, armature and I back contact of change-overrelay 11, conductor 82, back contact and armature 68 of relay 68,conductor 18, front contact and armature of relay 46 to the positivepole of battery. Connector relay 81 when thus energized is lockedoperated from the negative pole of battery, winding of this relay,conductor 88, front contact and armature I of relay 81, conductor 83,front contact and armature of relay 46 to the positive pole of battery.The release relay 66 is now operated, from the negative pole of battery,winding of this relay, armature and front contact of relay 88, conductor8|, front contact and armature of relay 81, conductor to the positivepole of battery."As soon as the release relay 65 is operated it opensthe locking circuits of the counting relays which have been operated, inthis case the number one counting relay 68.-

As soon as the tens connector relay 18 and the unitsconnector relay 81are operated, the called line #41 (Fig. 4) has its tip conductor 82, itsring conductor 83; and its sleeve conductor 84 extended thru thecontacts of these relays to the corresponding tip, ring and sleeveconductors 86,

-86 and 81 of the called and of the link circuit connect the ringingcurrent, Also when the which was seized by thecalling telephone line.The test-of the called line #41 is now made. it be assumed that thisline is idle at this time. Under this condition the change-over relay 11(Fig. 7) is actuated from the negative pole of battery, winding of relayll, conductor 14, armature and back contactof relay I3, conductor 12,armature and back contacts of relays 51 to 63' inclusive, conductor 96,upper winding of relay 99 (Fig. 6), front contact and armature of relay65, now operated, conductor 66, armature and back contact of releaserelay 49, conductor 61,, back contact and armature 98 of relay 69,conductor 19, front contact and armature of relay, to the positive poleof battery. The

operation of the change-over relay ll completes a circuit for operatingthe cut-in relay 69. This circuit extends from the negative pole. ofbattery, winding of the relay 69, its continuity spring and backcontact, armature and front contact of relay 11, conductor 9!, frontcontact and armature of relay 81, conductor 85 to the positive pole ofbattery. The relay 69 when operated closes a locking circuit for itselfthru its continuity spring and armature, conductor 79 to the positivepole of battery, at the armature and front contact of relay 45. Theoperation of the cut-in relay 69 interrupts the energizing circuits ofthe changeover relay H and of the transfer relay 99 which circuits, itwill be recalled, extend thru the back contact and armature 9B of relay69. The cut-off relay of the called line is operated over the sleeveconductor 94 of this line, sleeve conductor 91 of the called end of thelink connected thereto, front contact and armature 68 of relay 99,conductor 79 to the positive pole of battery at the armature and frontcontact of relay 45. the sleeve conductors 91 and 99 provide a busypotential for rendering thecalled line busy.

It has been mentioned that the change-overrelay H is slow-releasing andtherefore before it retracts its armatures, a circuit is completed forthe ringing relay 99, from the negative pole of battery, resistance,winding of this relay, front contact and middle armature of thechange-over relay ill, sleeve conductor 91, which it will be recalled isnow connected over conductor 19 to the positive pole of battery at thearmature and front contact of relay 45. The ring relay 99 as soon as itis operated, closes a locking circuit for itself thru its lower frontcontact and armature, holding conductor 10 to the positive pole ofbattery at the armature and front contact of relay 45.

On the operation of the ringing relay 99, in terrupted ringing currentis applied to the tip and ring conductors 95 and 99 of the called end ofthe link circuit in use'and thence to the corresponding conductors ofthe called line which include the ringer of the called line. Theconductors 95 and 9B are connected to the-ringing generator thruarmatures and front contacts of the cut-in relay 99 and ringing relay99. It will be understood that ringing circuit leading to the ringing,generator (not shown) includes the ringing trip relay E99. Interruptedringing cur rent is applied to the ringer (not shown) at the calledsubstation over the circuit 'just described, until the called partyresponds by removing his receiver from the switch hook. When this takesplace the marginal trip relay I is operated and at its armature andfront contact closes a shunt circuit about the ringing relay 99 causingthis last-named relay to release and thereby dis- The positive batterythus applied to ringing relay 99 releases, the battery feed relay NH ofthe called end of the connection is connected in series with thedifferentially wound relay )2 to the tip and ring conductors 95 and 98of the called end of the link.

The release of the telephone connection just completed is efl'ected bythe calling subscriber when he replaces his receiver on its switch book.This act opens the line circuit at the switch hook contacts and therebyeffects the release of the impulse relay 44 and in turn the slowreleasing relay 45. It will be recalled that the relay 45 when operatedapplied the positive pole of bat! tery to the holding conductor I0. Thuswhen the positive pole of battery is disconnected from the holdingconductor 19, the tens connector relay 78, the units connector relay 81and the tens finder relay 3| as well as the units finder relay 32 arereleased. The relay 45 also opens the sleeve conductor 42 of the callingline and therefore efiects the release of the calling cut-oil relay 8.Likewise, the release of the relay t9 effects the release of the relay55 as well as the cut-off relay of the called line because the circuitof this last-mentioned relay which extends to the positive pole ofbattery over the sleeve conductor of this line, is interrupted'at thefront contact and armature of relay t5.

- In the event that the called line was busy at the point in theoperation when it was tested, then the positive pole of the batterywould be connected to the sleeve conductor of that line either over aconductor similar to conductor ti,

and calling end of the link to the positive pole of battery at thearmature 52 and front contact of relay 45, or over a conductor similarto the sleeve conductor 91 of the called end of the link and thence overthe holding conductor it to the positive pole of battery at the armatureand front contact of relay 45. Referring back to the time when the unitsconnector relay 9? was operated, a circuit is closed for operating therelay 990i the link circuit. The operating circuit for the relay 49extends from the positive pole of battery on the sleeve conductor of thecalled line which extended thru the armatures and contacts of the unitsconnector relay 8! and the tens connector relay-18 to the sleeveconductor 97 of the link, armature and back contact of the change-overrelay 11, conductor I09, back contact and armature of relay 69, backcontact, continuity spring and winding of the release relay 49,conductor I94, winding of the busy relay I09 (Fig. 2) to contact andarmature of the cut-0E relay 8 and thence thru the calling subscribersreceiver at the calling station and then over the telephone lineconductor II to the positive pole of battery at the armature and backcontact of the cut-oi! relay 8. r

It should be pointed out that the change-over relay 1! cannot beenergized to initiate the selection of the called line now'assumed to bebusy, inasmuch as the change-over relay circuit is now open at the backcontact and armature of the release relay 49. 'Since the change-overrelay 11 cannot be operated under the conditions asthe conductor 9s'umed, the cut-in relay 69 and the ringing relay 99 will not beenergized to eflect the application of ringing current. holding circuitof the tens finder relay 3| and the units finder relay 32 include theconductors 48 and 50 which are normally connected in series thruthelowermost armature and backcontact of relay 49. Therefore when therelease relay 49 is energized the holding circuits for these finderrelays are interrupted so that they release to disconnect the callingline from the selected link. The cutoff relay 8 (Fig. 2), of the callingline which was maintained operated over the sleeve conductor 39 of thecalling line and the sleeve conductor 92 of theselected link also hasits circuit interrupted when the finder relays disconnect the callingline from the link. In addition the disconnection of the link from thecalling line interrupts the operating circuit of the impulse relay 44which releases and in turn effects the release of the slow releasingrelay 45. Relay 45 on deenergizing effects the release of the variousoperated relays of the link in the manner previously described.

When the cutoff relay 8 releases in the manner just mentioned, thecalling line circuit including is extended thru the armatures and backcontacts of the cutofi relay 8, armature, front contact and lefthandwinding of the relay 1 and thence thru the righthand winding of the busyrelay 185 which is common to a group of lines. The busy relay m9connects busy tone current to the calling line and the relay 1 remainsoperated to maintain the calling line disconnected from its line relayso that this line relay cannot now connect the calling line to anotherlink circuit. It will be appreciated that the cutoff relay 3 cannot beenergized while the receiver at the calling substation is off of itsswitch hook since the initial operating circuit of the cutofi relay ismaintained open at this time at the righthand armature and back contactof the relay 1. The energization of the busy relay I85 starts the busytone machine and the busy tone current is applied to the calling line bybeing induced from the lefthand winding of 'the relay Hi5 into the Itwill be recalled that the digit impulse, the system operates aspreviously described to effect the operation of the number one countingrelay 58. At the end of the tens series of impulses the number one tensconnector relay I01 is operated and locked operated in a manner similarto that already described. In response to the single units impulse thenumber one counting relay 58 is again operated andin this instance iseffective to complete a circuit as previously described for operatingthe number one units connector relay 81. The energization of theselast-mentioned connector relays extends the link circuit, which isconnected to the calling line, to the code call unit shown in Fig. 2a.The positive pole of battery is connected at this time to the sleeveconductor I08 of the code call unit, which conductor includes thewinding of the start relay I09 and is connected to the negative pole ofbattery. The start relay ")9 at its front contact and armature completesa circuit for starting the code call current generator (not shown). Itwill be noted that the tip conductor H0 and the ring conductor III ofthe code calling network are connected thru the impedance coil H2 sothat this closed circuit across these conductors actuates the trip relayI90 to prevent ringing current from the link being applied to the codecall network. If the calling party does not hear a busy tone signal inhis telephone receiver at this time, he knows that the code call isidle, and he then proceeds to dial the code of impulses assigned to theparty wanted. For example, he may dial the digit two twice in order togive two short rings or he may dial 0 twice to righthand winding thereofto which winding the a calling line is connected. When the callingsubscriber replaces his receiver on its switchhook the telephone linecircuit is opened whereupon the slow releasing relay 1 releases and allof the circuits employed in the telephone connection under considerationare restored to their normal condition.

The present system is arranged so that a party at any station of thesystem can establish code call conditions whereby signals such as bellsor lights or both may be operated according to predetermined codes inorder to locate various persons in a plant where the system may be used.In effecting the code operation of the system, a party desiring toinitiate code call signals, is instructed to dial a predeterminednumber. In the system herein disclosed the predetermined number isassumed to be #11. It will be understood that the use of #11 for thecode call prevents the use of this number for a subscribers line. Thesubscriber, after removing his receiver from the switchhook and afterreceiving the dial tone indicating that his line has been connected toan idle link circuit, first operates his dial sender to transmit oneimpulse corresponding to the give two long rings. of cours it will beunderstood that various codes of long and short impulses may be assignedfor use in signalling various parties. The core call impulse circuitextends from the negative pole of battery, winding of the relay H3,conductor il' i, front contact and armature of the units connector relay81, front contact and armature of the tens connector relay ifi'l,conductor H5, uppermost armature and front contact of relay Nil,conductor lit,

back contacts and armatures. of the counting relays 92 to 51 inclusive,conductor 16, front contact and armature of relay 55, back contact andarmature of the relay impulse i l, conductor 66, back contact andarmature of the trunk release relay 91, to the positive pole of battery.Thus on each deenergization of the impulse relay 44 in response to eachof the code impulses transmitted by the calling subscriber, an impulseis transmitted over the last-described circuit to the pulse relay H3. Itwill be noted that the relay 3' is slow releasing and will remainoperated during a series of properly timed impulses. Thus it will remainoperated for a comparatively long interval of time when the #0 digit isdialed and will remain operated for a comparatively short interval oftime when the digit two is dialed. The operation of the relay H3 appliesgenerator current thru its armatures and front contacts to theconductors H1 and H8 across which the code call signals such as l'l9 areconnected in multiple. Thus the signals herein shown illustrated asbells ring the predetermined code at their various locations. When thewanted party hears his code on the common code bells H9 he answers bydialing a predetermined number, e. g. the number 12. The partyanswering, of course, goes to the nearest telephone'and removes thereceiver from the switchhook thereat, which results in connecting thisline to a second link cirto .the single tens cuit. The desired partythereupon sends impulses-according to the number 12 which, of course,operates first the number one counting relay associated with the linkcircuit connected to his line and the operation of this relay'efiectsthe energization of a number one tens connector relay similar to II". Inresponse to the units digit #2 the counting relay 59 is likewise oper-'ated in the manner already described. The operation of this countingrelay causes the operation of a number two units connector relay similarIto I20. The operation of the mentioned tens and unit connector relaysextends the line #12 to the link circuit thathas been used by. thecalling party. As soon as this connection has been established positivepotential on the sleeve conductor I2I energizes the make busy relay I22which relay at its armature. and front contact connects the positivepole of battery to the sleeve conductor I08 connected to the link usedby the calling telephone line, thereby maintaining the code call numberbusy until both parties to the connection have replaced their receiverson the switchhooks. The tip and ring conductors at the calling end ofthe link used by the answering party are thus connected to the tip andring conductors of the calling end of the link used by the calling partybecause these are common to the code call circuit.

Thus a talking connection is established between the callingand thecalled parties. The release of the connection used by the callin partyreleasesthe link and the other apparatus used by him and a link andapparatus used by the answering party is similarly released when theanswering party hangs up. The release of both of these connectionsrestores the code call apparatus to normal condition.

In accordance with the present invention it is proposed to provide fortrunk call connections from the present system either to a distantmanual telephone ofiice or to a distant automatic telephone office bymeans of two-way trunks between the present system and. a central ofllceof either of the mentioned types. lines in the present system may bearranged to have restricted or unrestricted connection to the mentionedtrunks, that is certain of the telephone lines can obtain connection tothese trunks while other lines of the system are so arranged that theycannot be connected to said trunks. Let it be assumed that a callingparty on a tele- The telephone phone line arranged for unrestrictedservice, de-

sires connection to a trunk leading to a distant ofice. This subscriberis instructed to dial a predetermined number, for example, #55, toselect the first idle trunk leading to the central oflice (Fig. 3).However, in the case of incoming calls from the distant central ofilce,the central omce operator plugs into an idle trunk and ringing currentapplied to this trunk is effective to operate one or more bells in thepresent automatic exchange. Any person hearing these bells can answerthe incoming trunk call by removing the receiver from the switchhook ofany telephone line in the system and dialing a predetermined number, forexample, the #66.

Let it be assumed that it is desired to initiate a call from anunrestricted telephone line in the system to a distant exchange. Thesubscriber does this by removing his receiver from its switchhook and assoon as he hears the dial tone he dials the predetermined trunk number55. On removing the receiver from the switchhook, the apparatus operatesto extend the calling line to an idle link circuit thru the operation ofa tens finder relay and 2. units finder relay in a manner previouslydescribed in extending a call between local subscribers. As soon as thelinkis connected to the calling line, the dial tone is applied to thisline and the subscriber operates his dial sender to transmit five tensimpulses; In response to these five impulses the counting relays areoperated in a manner already described to energize the #5 counting relayB2. In response to the operation of this relay the tens connector relayI23 is operated in manner similar to that already described. The callingsubscriber then transmits five units impulses corresponding to the unitsdigit of the predetermined number 55. In this instance the countingrelays of the selected link will attempt to count the five units impulseof the second or units digit but the counting will be stopped and thecorresponding counting relay will be locked operated at the first idletrunk in the group of five trunks leading to the distant ofiice. Inother words if trunk number one is idle, only one of the five unitsimpulses will be effective to operate the counting relays and theremaining four impulses will be ineffective. However, if trunk number 5is the first idle trunk then all of the five impulses oi the units digitwill be counted and the number 5 counting relay 62 will be operated andlocked. If all five trunks of the group are busy then all of the fiveunits impulses will be counted but a busy circuit will function tosignal the calling party that all of the trunks in the group are busy.

Let it be assumed that the trunk illustrated in the drawings (Fig. 3) isthe number one trunkand that this trunk is idle.- Under this conditionwhen the subscriber transmits five impulses of the units digit theimpulse relay 44 will release five times after which it will remainenergized. The first release of the relay M in response to the firstimpulse is efiective to operate the number one counting relay 58 atwhich time the relay 5'! releases when the relay 44 operates at the endof the first impulse. Since the trunk number one is assumed to be idlethe relay I3 is now operated from the negative pole of battery, windingof relay I3, armature and front contact of the number one counting relay58, conductor I25, front contact and armature of the tens connectorrelay I23, conductor I26, back contact and armatur of the make busyrelay I21, conductor I28, back contact and armature of the slowreleasing relay I 29 (Fig. 3) to the positive pole of battery. Thisoperation of the relay I3 opens the circuit including the conductor I2so that the remaining counting relays of the series will not be operatedin response to impulses, that is the remaining four impulses are of noeffect. In the event that the first four trunks of the group of fivetrunks are busy, the relays similar to I29 thereof will be energized sothat no circuit will be completed for operating the relay I3. Whenhowever, the fifth units impulse is recorded on the number five countingrelay 62, the relay I3 will be operated in a circuit similar to thatdescribed but in this instance will be complete from the back contactand armature of a relay similar to I29 at the fifth trunk of the group.

Since it has been assumed that the first trunk is idle and only oneunits impulse effectively registered, the units connector relayii'i willbe operated over a circuit as described so that the trunk #1 will beselected although the number 55 has been dialed. At the conclusion ofthe operation of the counting relays, the release relay 65 is operatedover the conductor 9i, its circuit being completed at the front contactand armature of the connector relay 81. With the relay 65 energized, theoperated counting relay, in this instance the number one counting relay58, is released since its holding circuit is interrupted at the armatureand back contacts of relay 65. Thechange-over relay 11 is now operatedfromthe negative pole of battery, winding of this relay, armature andback contact of the relay 13, conductor 12, armatures and back contactsof relays 51 to 63 inclusive, conductor 86, upper winding of the relay80, front contact and armature of release relay 65, conductor 66,armature and back contact of relay 49, conductor 61, back contact andarmature 68 of relay 69 and thence over the holding conductor 19 to thepositive pole of battery at the front contact and armature of relay 45.When the change-over relay 11 operates, cut-in,relay 69 and the ringingrelay 99 are operated as previously described. A circuit is nowcompleted from the negative pole 'of battery, resistance, back contactand armature of the make busy relay I21 (Fig. 3), conductor I30,armature and front contact of the units connector relay 81, conductorI3I, lefthand winding of the relay I99, conductors I32 and I33, frontcontact and armature of the number five tens connector relay I23,conductor I34 and conductor 91, front contact and armature of relay 69and thence over the conductor 18 to the positive pole of battery at thefront contact and armature of relay 45. in turn operates the findermarking relay I35 (Fig. ,3). This circuit extends from. the negativepole of battery, winding of the relay I35, conductor I36, front contactand armature of the relay I99, armature and back contact of the relayI31 which is common to the group of trunks, to the positive pole ofbattery. With the finder marking relay I35 operated the trunk markingRelay I99 operates and relay I38 is energized in a circuit from thepositive pole of battery, winding of this relay, conductor I39, armatureand front contact of the units connector relay 81, conductor I48,armature and front contact of relay I99, conductor I4I, front contactand armature of relay I35, conductor I42, righthand winding of the relayI99 to the negative pole of battery. This circuit operates the trunkmarking relay I38 and holds the relay I99 operated.

At this time the tens finder relay I44 (Fig. l) and the units finderrelay I of the number one trunk are operated to connect this trunk tothe calling line number II. Relay I44 is operated in a circuit from thenegative pole of battery, winding of this relay, armature and, frontcontact of the trunk marking relay I38, armature and front contact ofthe finder marking relay I35,

conductor I46, and 33, frontcontact and armature of tens finder relay3|, conductor 48, back contact and armature of the release relay 49,conductor 58, front contact and armature 5I of the slow releasing relay45 of the link. Similarly the units finder relay I45 is energized in acircuit from the negative pole of battery, winding of this relay,armature and front contacts of relays I 38 and I35, conductors I41 and35, front contact and armature of units finder relay 32 and thence overconductor 48 and the remainder of the circuit already described to thepositive pole of battery at the front contact and armature 5| of relay45. The operation of the tens and units finder relays I44 and I45extends the tip, ring and sleeve conductors 31, 36 and 39 of thesubscribers line #11 to the tip, ring and sleeve conductors I46, I41 andI98 of the trunk, thence thru both windings in series of the relay I48(Fig. 3) of the trunk, conductors I49 and I59, back contacts andcontinuity springs of the holding relay I5I thru both windings in seriesof the differentially wound relay I52 from whence one side of thecircuit is extended thru the continuity spring and back contact of therelay I53, Winding of the relay I54 to the positive pole of battery. Theother side of this circuit is extended from the lower winding of thedifferential relay I52, back contact and inner armature of relay I54,trunk line conductor to the distant office, armature and backcontact ofthe cut-off relay I55 associated with the operators trunk circuit,winding of the line relay I56 also associated with the trunk circuit, tothe negative pole of battery. Differential relay I52 does not operate atthis time but the line relay I56 operates to signal the operator whoplugs in an idle cord circuit to the related trunk. The relay I 48 isalso energized in this circuit and at its inner front contact andarmature it completes a circuit for operating the slow releasing relayI5 1. The relay I51 at its inner upper front contact and armaturecompletes an operating circuit for the slow releasing relay I29. RelayI29 on operating, completes a circuit from the positive pole of battery,its armature and front contact, conductor I58, armature and back contactof relay I 18, armature and front contact of the tens finder relay I44and winding of this relay to the negative pole of" battery and inmultiple therewith thru the armature, front contact and winding of theunits finder relay I45 to the negative pole of battery. Theselast-described circuits function to lock the finder relays in operatedcondition.

Referring back to the point in the description moves positive batterypotential from the relays such as I99, I60, I6I and I62 to prevent theoperation of other finder mar king relays such as I35,'at the same timein the event that several trunk calls are initiated simultaneously.Trunk release relay 41 (Fig. '1) is now operated from the negative 'poleof battery, winding of this relay, conductor I63, front contacts andarmatures of finder marking relay I35 and of trunk marking relay I38 aswell as of the tens finder relay I44 and the units finder relay I 45, tothe positive pole of battery. Trunk release relay 41 when operated locksitself in this condition thru its inner front contact and armature,front contact and armature of relay 45, to the positive pole of battery.However, the operation of the trunk release relay, at its uppermostarmature and back contact, interrupts the energizing circuit includingthe conductor 46 leading to the slow releasing relay 45. When the relay45 releases, it removes the positive potential which has been holdingthe relays 3|, 32 (Fig. 8) of the finder and relays 55, and 53 of thelink, tens connector relay I23 and the units connector relay 81, as wellas the cut-in relay 69, the ringing relay 99 and the finder markingrelay I35, thus all of these relays also release. Trunk release relay 41also releases because its holding circuitis openedat the relaydisconnects the link in use, from the calling line and thus the impulserelay ll releases. Relays I38 and I89 are also released by the releaseofher cord circuit into the trunk jack, the contacts of which aredesignated I6I and I62, the'cut-off relay I55 of this trunk is operatedin the wellknown manner to disconnect the line relay I66 and toextinguish the trunk signal (not shown). Current from the cord circuit(not shown) at the central office is now applied to the tip contact I6Iof the plug, back contact and continuity spring of the relay I53,conductor I63, front contact and armature of relay I51, conductor I66,winding of the relay I53 to the negative pole of battery. Relay I53 isthus operated and its continuity spring and armature completes a lockingcircuit for itself independent of the battery supply at the operatorscord circuit. With the relay I53 operated it interrupts'the circuit ofthe relay I54 which releases.

From the foregoing it will be seen that the link circuit originallyconnected to the calling line to establish this connection is releasedand that the calling line is ,connected directly thru the contacts andarmatures of the finder relays I and-I65 to the trunk circuit leading tothe central office.

When the subscriber at the localstation designated #11 terminates theconnection by replac-.

ing his receiver on its switchhook, the tip and ring conductors leadingto the central office are opened and this effects the release of therelay I48 of the local trunk circuit. This gives the central officeoperator disconnect supervision, also the release of the relay I48causes the slow releasing relay I51 to deenergize. Relay I51 onreleasing, opens the locking circuit of the relay I53 and connects thehigh resistance relay I65 across the trunk. Thus relay I53 releases andrelay I65 operates. When therelay I65 operates, it closes a circuit forholding the slow releasing relay I29 before it has had time to release,following the'release of the relay I51. Since relay I29 is thus heldoperated, the trunk still tests busy and the cut-off relayB of the localline #11 is still held operated. The operated make busy relay I21 (Fig.3) keeps this trunk busy by disconnecting the negative pole of batteryat its back contact and armature. It will be understood that the makebusy relay I21 is locked operated thru its inner front contact andarmature, conductor I66, front contact and armature of relay I29 to thepositive pole of battery. When the, central oillce operator disconnectsby removing the plug of her cord circuit from the jack which includesthe contacts I6I and I62, the trunk circuit is opened which allows thehigh resistance relay I65 to release. This relay in turn effectsthe'release of slow releasing relay I29 and relay I29 then eifects therelease of the tens finder relay 3|, the units finder relay 32 and themake busy relay I21. The tip and ring conductors of the local line #11are now opened because the finder relays I44 and I45 of the trunk arereleased.

In the case of a call originated at the distant central oilice andintended for a subscriber at the local automatic exchange, the operatorat the central oflice'plugs her cord circuit into the trunk jack of thefirst idle circuit leading to the local automatic exchange. As a resultof plugging into this trunk jack, battery connected at the cord circuittaken for use is applied across the trunk conductors for operating thehigh resistance relay- I65. When the operator applies ringing current tothe trunk to signal the local automatic exchange, this alternatingringing current operates the relay I61. The slow releasing relay I29 isoperated as a result of the operation of either of these last-mentionedrelays. The relay I29 makes this trunk busy to outgoing calls because itremoves positive potential from the conductor I28. However, this trunkis selectable at the local exchange by the local substation which isassigned to answer such incoming calls.

This trunk is rendered selectable because the relay I28 applies positivebattery, at its armature and front contact, to the conductor I66 whichit will be noted is extended thru the inner armature and back contact ofthe make busy relay I21. The operation of relay I61 by the ringingcurrent intermittently connects local uninterrupted generator current tothe common bell circuit for signalling the attendant who is assigned toanswer incoming calls. I

The party at the local automatic exchange who is responsible foranswering calls from a distant ofiice now removes the receiver from theswitchhook and operates the dial sender at the substation to transmitimpulses corresponding to #66. The removal of the receiver from theswitchhook causes the telephone line of this assigned party to beselected by the first idle link circuit. On the completion of thisconnection of the link to the mentioned line, a dial tone informs theparty that he can proceed with dialing the number 66. In response to thesix .impulses corresponding to the tens digit #6 the counting relays 58to 62 inclusive are operated and released while the number 6 countingrelay 63 is operated and is maintained operated at this time. Theoperation of the number 6 counting relay 63 causes the operation of thenumber 6 tens connector relay I68 (Fig. 4). At the close of the-tensseries of impulses and after the operation of the tens connector relayI68, the counting relays are restored to their normal position aspreviously described, in readiness to receive the impulses correspondingto the unit-s digit of the number 66. In response -to these unitsimpulses the number one counting relay 58 is operated and as soon asthis takes place the relay 13 is operated from the negative pole ofbattery, winding of this relay, front contact and armature of thecounting relay 58, conductor I25, front. contact and armature of thetens connector relay I63, conductor I69, back contact and armature ofthe make busy relay I21, conductor l66, front contact and armature ofthe circuits then function in the previously described manner, forselecting this trunk after which the trunk connects itself to thecalling line by way of its finder relays and the link is released.Supervision and release operations are now controlled in the mannerdescribedior an outgoing trunk call.

The above description relates to a local telephone line which isequipped for non-restricted service, that is, it can make calls over atrunk to ple with the high resistance such as I10 (Fig. 2)

In the case of such a line which is equipped for only limited service,the marginal relay 53 of the selected link will not operate. In such acase when the trunk number 65 is dialed, positive battery at thearmature and back contact of relay 53 is extended over conductor IH,armature and front contact of the tens connector relay I68, conductorI34 to the sleeve conductor 91 of the link. Thus when change-over relay11 releases at the close of the series of impulses, the

circuit including conductor 91 is extended, thru the armature and backcontact of relay 11, conductor I03, back contact and armature of thecut-in relay 59, back contact, continuity spring and winding of therelease relay 49, conductor I 3, winding of the busy relay I85. Therelease relay 69 is energized in series with the busy relay I05. Releaserelay d9 when operated efiects the disconnection of the calling linefrom the link which it has seized. The calling line is now connected tothe winding of its associated relay 7, and busy tone is supplied to thislineuntil release, as previously described.

. Provision is made in the present system so that either an outgoingtrunk call'or an incoming trunk call can be transferred by certain ofthe substations of the local automatic exchange to other local lines. Inorder to effect such trans- .fer the local substation must be providedwith a push button such as I1I enabling one side of the calling line tobe connected to ground. For convenience in describing the operation ofthis transfer feature, it will be assumed that the calling line numberII is connected to a central office trunk which connection has beencompleted in the manner already described. It will further be assumedthat the party connected to the trunk circuit at the distant exchangefinds that his connection should be transferred to line number I5. Itwill be remembered that with the line number II connected to the firsttrunk, namely trunk number 5I, tens finder relay I44 and the unitsfinder relay I45 will be operated.

Also the relays I48, I51, I29, I53 and I21 of the trunk will be operatedin the manner already described. Each of the trunk conductors to thedistant ofiice will be energized thru the plug contacts I6I and I62.However, at this time the relays I54 and I65 are not energized. Now whenlines.

the subscriber at substation number II, receives button I'II momentarilyand then dials the num ber I5. The actuation of this bush button groundsone side of the telephone line circuit which is effect/iveto unbalancethe differential relay I52 of the trunk so that this relay operates.When the relay I52 operates it closes a .short circuit across its upperwinding so that when once energized, it will remain operated even thoughthe push button III is released. The upper contact and armature of thedifferential relay I52 connects the conductors I12 to I13 leading to thelookout circuit for the several By this arrangement, the differentialrelay I52 acts in the same mannera a line relay of the telephone lines,and thus causes the'operation of the tens lock-out relay I1 and theunits lock-out relay I3. These two lock-out relays when operated, causethe allotter repeater relay such as 58 of the first idle link, to beoperated which is assumed to be link number 2. The operation of therelay 58 causes the tens finder relay I15 and the units finder relaysuch as 32 of the second link to operate to connect the tip, ring andsleeve conductors of trunk number 5| to the tip, ring and sleeveconductors of link #2. The impulse relay similar to 44 of link #2 isenergized over the tip and ring conductors of the calling line circuit.Relay M in'turn causes relays similar to 45 and 55 of this link to beoperated. On the operation of the relay 35, relay I5I of the trunk isoperated, because the sleeve conductor of the trunk is connected topositive battery at link number 2 and is extended thru the finder relaysand thence by the sleeve conductor of the trunk to the Winding of theholding relay IEI. Relay I5i at its make before break contacts connectsa resistance coll I16 across the trunk conductors leading to the centralomce, for the purpose of holding this trunk and for providingsupervision. If the push button I'II has been released by this time,then the opening of the back contact and armature of the holding relayI5I establishes a balanced circuit through the windings of thedifferential relay I 52 for causing this relay to release. When therelay I5? is thus released it opens the operating circuit of the tenslock-out relay I1 and the units lock-out relay I3. However, the trunk isstill held because the holding relay I5I is still operated. Theconductors I16 and I11 leading from the relay I68 of the trunk areextended thru the units finder relay such as 32 and a tens finder relaysuch as I15, to the corresponding tip and ring conductors 40 and 4| ofthe second link, which last-named conductors are connected in seriesthru the upper and lower windings of the differential relay 43 and theimpulse relay 44 respectively to the negative and positive poles ofbattery. The party at station number I I now dials the number l5corresponding to the number of the substation to which the call is to betransferred. In response to each of the series of impulses correspondingto the digits of the number 15, the impulse relay 44 successivelyoperates the counting relays so that the tens connector relay I01 andthe units connector relay I84 are operated to connect the line ofsubstation number I5 to this second link. Ringing current is thensupplied to the telephoneline number I5 and when the subscriber thereatanswers by removing his receiver from its switchhook, the ringingcurrent is disconnected and the subscriber at station number I5 is intelephonic connection with the subscriber at station number II. Thislast-named subscriber advises the subscriber at ture of a tens finderrelay similar to I15 to the positive pole of battery. It will berecalled that station number I5 that a call is waiting him on the trunk.This latter subscriber then operates his push button similar to thatshown at I" to ground one side of the telephone connection. Thisoperation is effective to unbalance the differentially wound relay. I02ofthe second link causing this relay to operate. When relay I02 isoperated, a circuit is completed for operating the trunk release relay41. This circuit is traceable from the negative pole of battery, windingof relay 41, front contact and armature of the relay I02, front contactandarmature of the relay IOI (now operated) back contact and armature ofthe differential relay 43, conductor I83, front contact and armature ofa tens finder relay similar to I15 which relay has cooperated inconnecting line number II to line number I5.

Trunk release 41 when operated locks itself in this condition at theinnermost front contact and armature of relay 45, to the positive poleof battery. The release relay I18 of the trunk is now energized from thenegative pole of battery, winding of this relay, conductor I19, armatureand front contact of the units finder relay such as 32, armature andfront contact of a tens finder relay similar to I15, conductor I80,front contact and armature of differential relay I02, back contact andarmature of differential relay 43, conductor I83, front contact andarmature of a relay similar tov I15 to the positive pole of battery. Theoperation of the relay I18 opens the locking circuits for the finderrelays I44 and I 45 of the trunk circuit so that the telephone linenumber II is disconnected from the trunk and is transferred back to itsown line circuit. It will be recalled that at this time the relay 1 islocked-energized in series with telephone line number II. Since thecutoff relay 8 has been released by the disconnection of the line numberII from the mentioned trunk, relay 1 while thus operated, maintains busypotential over the sleeve conductor 39 to maintain this line busy untilthe subscriber thereat replaces his receiver on its switchhook. As soonas the relay 1 is operated it applies a busy tone to the telephone linenumber II which continues to sound in the receiver at substation numberII until the subscriber thereat replaces his receiver on the switchhookat which time the circuit of relay 1 is opened. This is effective toremove the busy potential from the sleeve conductor 39 and alsodisconnects the busy tone current from this line.

As soon as the telephone line number II is disconnected from thementioned trunk by the operation of the release relay I18, the relay I48of the trunk circuit deenergizes but the slow releasing relay I51of thistrunk has a substitute circuit completed for itself at this time at thefront contact and armature of relay I5I, Also when the release relay I18energizes it disconnects the telephone line number II from the callingend of the second link circuit so that the impulse relay 44 thereofdeenergizes.

When the push button similar to Hi at sub-- station number I5 isoperated and thenreleased, the differential relay I02 of the second linkretracts its armatures thereby closing a circuit for operating thetransfer relay I8I of this link. A circuit for operating the relay I8I(Fig. 8) extends from the negative pole .of battery,-winding of thisrelay, armature and front contact of relay 41, conductor I82, backcontact and armature of relay I02, front contact and armature of relayIOI, back contact and armature of differential relay .43, conductor I83,front contact and armawhen telephone line number I5 was selected bysubstation number II, a tens connector relay similar to I01 and a unitsconnector relay similar to I84 was operated, Corresponding finder relaysI44 and I81 of the two-way trunk are now operated to extend this trunkto telephone line number I5. The circuit for operating the tens finderrelay I44"of the trunk is traceable from the negative pole of battery,winding ofthis relay, conductor I85, armature and front contact of relayof a units finder relay such as 32, armature and front contact of a tensflnder relay such as I15, armature and front contact of transfer relayI8I, conductor I85, conductor I81, inner front contact and armature oftens connector relay I01, conductor 83, front contact and armature ofslow releasing relay 45 to theposltive pole of battery. The number 5units finder relay I81 is also energized from the negative battery,winding of this relay, conductors I88 and I89, armatures and frontcontacts of relays 32 and I15, armature and front contact of transferrelay IBI; conductor I90, conductor I9I,.front contact and armature ofthe number 5 units connector relay-I84, conductor 83 to the positivepole of battery at the front contact and armature of slow releasingrelay 45. The finder relays I44 and I81 when thus operated are heldlooked over a circuit including the conductor I58 which extends topositive battery at the front contact and armature of relay i29. Thisselection and operation of the trunk finder relays is of course madebefore the finder relays of the link and the transfer relay I8I release.

Also when the push button similar to "I at substation number I5isreleased, the release of the differential relay I02 effects therelease of the slow releasing relays similar to 45 and 55 at the secondlink because one circuit of relay 45 is opened at a front contact andarmature of the differential relay I02. The other branch oper atingcircuit of the slowreleasing relay 45 is opened at the back contact andarmature of trunk release relay 41 since this relay is now operated. Therelease of relay 45 effects the release of relay 55. The relays I15, 32,I01 and I84 of the second link are released by the release of relay 45at the second link. The relay 41 also deenergizes because its lockingcircuit is opened at the relay 45. However, relay 41 is slow releasing.Relay I8I is also releasedwhen the relay 41 deenergizes. The holdingrelay I5I of the trunk circuit is released because the relay 45 removespositive potential from the sleeve conductor leading to this ground. Thetrunk circuit is now connected to line number I5'and since the holdingrelay I5I is released, line number I5 is in telephone connection withthe trunk. Line number I5 is thus in control of the release I and of thesupervision of the-trunk circuit in the manner previously described totelephone line number II,

A further feature of this invention enables the transfer operation to beeffected among a series of telephone lines in succession provided eachof these lines has a push button similar to Hi and a ground connectionat its substation. The repeated transfer among the series of telephonelines in succession is effected. in exactly, the same manner as alreadydescribed since the transfer of the trunk from a first line such as linenumber II to a second line such as number I5 places line number I5 inexactly the same condition as

